Non-stationary irradiance properties in dynamic FSO links: a model and field tests study

Time-variant Free-Space Optical channel behaviour is analysed for temporal variations of C²_n values, satellite motion and satellite passes. These variations lead to non-stationary statistical properties of the irradiance at the receiver. The analyses are based on representative link models and complemented by measured data from recent test campaigns. These are the 10km's near-horizontal field test with the TOMCAT demonstrator terminal and the in-orbit test between the SmallCAT terminal onboard the NorSat-TD LEO microsatellite and the TNO optical ground station GOCAT in The Hague. The study shows substantial variations of the statistical properties of the irradiance for LEO satellite motion and predominantly for time-variant C²_n behaviour. For variations of satellite passes–with respect to the ground station–the sensitivity of irradiance properties over the full pass is less pronounced. An analysis of the probability distribution of elevation angles over all satellite passes reveals a high probability of low elevation links.